1. Field of the Invention
The present invention relates to opto-electric measuring devices, and in particular such devices for measuring the attitude or position and dimension of objects by generation of a digital pulse train having pulses with a temporal position corresponding to the position of the object to be measured.
2. Description of the Prior Art
Opto-electric measuring devices utilizing a collimated beam of parallel light rays which is directed at an object to be measured are known in the art, such as the optical measuring apparatus disclosed in U.S. Pat. No. 3,765,774 and in U.S. Pat. No. 3,905,705. Conventional optical measuring devices of this type have a light source which emits a highly concentrated light beam which is deflected into a scanning plane by the use of a rotating mirror driven by a motor. The rotation of the mirror directs the beam toward a collimating means from which the light emerges in parallel rays to scan an object to be measured. A converging lens collects the parallel beams and directs them at a photoelectric detector which is connected to circuitry for generating electric signals whose temporal gap corresponds to the rotating velocity of the motor and which are interrupted by blockage of light as the beam sweeps over the object to be measured. A pulse generator controls a counting device which is combined with a gap signal for generation of a final gap signal which is then displayed.
In conventional optical measuring devices of the type described above, the pulse generator serves not only to supply an input level for a logic circuit or gate circuit which is pre-connected to the counting device and which receives a second input level from the detection device for the light beam, but also to drive the motor for rotating the mirror. The motor may, however, be subject to fluctuations in its mechanical rotary motion which are transmitted and amplified to the deflection motion of the light beam comprising the scanning sweep. Precise measurement operation requires an exact, predictable relationship between the inputs to the gap signal generating logic circuit, i.e. the inputs thereto received from the detection device, and the pulse generator. Inasmuch as the detection device derives its output signals from the light beam scanning motion which impinges thereon, unmeasured random fluctuations destroy the predicted relationship between the inputs to the logic circuit, thereby introducing error into the measurement.